I have a 2000 with the same tire size. My speedo reads high. At highway speeds it is off by 4 to 5 mph. This is compared to what the ECU thinks it is going and the radar speed signs. At 3500 it is just around 80.
Green 2000 SVT #1166
mods-K&N and Custom heat shield, optimized y pipe, Magnaflow center resonator, DMDhttp://www.geocities.com/savinoss/Cars.html
-Wifes car 99 Mystique V6 5 spd